Production of vanadium trioxide for the manufacture of ductile vanadium



Feb. 22, 1955 J. c. R. KELLY, JR y 2,702,739

PRODUCTION OF VANADIUM TRIOXIDE FOR THE n MANUFACTURE OF DUCTILEVANADIUM Filed Sept. 7, 195] 0PPe01/M0rf 004 05 w r//f aas-ENCETEMPEeH/'z//Fe- 0F' Graaff/0M INVENTOR .7. c'. e. Kauf fr.

Unite y States ThisV invention relates to vanadium, and morevparticularly 'to the production of such metal of an exceptionally liighdegree of purity, and vto an improved method for the Vmanufacturethereof.

The principal object of my invention, generally considered, is toproduce vanadium by reaction of a low valence compound thereof, producedby a low-temperature reduction of vanadium pentoxide, with calcium ormagnesium, said reaction taking place in a cup enclosed inav container,said container being lilled with an inert gas, as distinguished from theprior practice of reducing Yvanadic oxide in a heavy-walled iron bombwith agroundin stopper, said 'bomb being heated vin open air.

Another .object of my invention is to produce vanadium powder by heatinga vanadous or hypo-vanadous compound, produced by a low-temperaturereduction of vanadium pentoxide, mixed with calcium and/or magnesium andthe chloride of one or a mixture of said metals, by high-frequencyinduction, the reaction cup being enclosed in al .quartz or glass belljar, that is, one of 96% silica glass, sometimes designated by theCorning .trade mark Vycon A further object of my invention is to treatthe powder, produced in accordance with the above, to consolidate itinto .coherent metal and form to the desired shape.

A still further object of my invention is to producelow-nitrogen-content vanadium trioxide by reduction of vanadium-pentoxide, while keeping the temperature of vreaction low, as byfurnace control, preferably also vhumidifying the ,hydrogen or otherreducing atmosphere to `still Yfurther eliminate nitrogen, orhumidifying the reducing atmosphere while not changing the temperatureof reaction.

Other objects and advantages of the invention will become apparent asthe .descriptionproceeds Referring .to .the drawing:

The sole figure includes two curves, the upper one showing how thenitrogen contamination in the product varies with the temperature Vofreduction of vanadium .pentoxide `.to vanadium trioxide in the absenceof hydro- :gen humiditication, and .the lower one showing the beneiicialeffect of such humidication.

The reduction yby calcium of vanadium pentoxide, has .previously beenaccomplished in heavy-wall iron bombs with va ground-in stopper held inplace lby a screw cap. Such devices have a number of limitations anddisadvantages, to wit:

It 'is'diicult to maintain an air-tight joint between the stopper andbomb and to prevent reoxidation of the vanadium powder produced as thebomb cools, or during the heating process. Considerable warping of thebomb occurs `during heating and cooling, thus necessitating time-,consuming lapping operations between runs. The construction of bombshas been limited to materials which will resist oxidation at elevatedtemperatures, and iron or iron alloys have lbeen generally used foreconomy. Bombs were without exceptionof heavy-Walled construction toIpermit sufficient surface area for sealing and presumably to withstandpressure produced in the reaction.

From thermo-chemical data and a consideration `of 4the products formedin the reaction between vanadium trivoxide (or lower valence oxide, suchas the dioxide, V202) which the inventors Gregory et al., named incopending application Serial No. 138,124, tiled January l2, 1950, nowPatent No. 2,653,869, have substituted for the pentoxide, previouslyemployed, and calcium, lthey concluded that the pressures developed inthe reaction were insufficient to necessitate the heavy-walled bombsprevilously used. They tested their conclusions by placing'an "iron cup,lined with non-'reactive refractory material,

such as CaO or MgO under a Vycor (or quartz bell jar, evacuating thebell jar, and thenhea-ting the .cupby high-frequency induction 4to causethe calcium ytoxrediice the vanadium oxide. Vaporization of' the calciumwas suppressed by filling the jar with argon gas at a pressure slightlyless than atmospheric. There'was'no abnormal pressure produced duringthe reaction, very littlel vapor"- ization of calcium, and satisfactoryvanadium metal powder was obtained. s

The reduction of vanadium pentoxide 'bycalcium is old in the prior art.However, the vanadium so produced, contained substantial quantities ofmetallic beads, apparently formed from fused metal. Although Sonie ofthe individual beads were-soft and ductile, otherls'were not and themix-ture of line-powder and fused beads when pressed and sinteredyielded hard and brittle metal compacts. The result Vhas been due toAthe non-recognition of the importance of controllingr both the amountof calcium present andthe temperature of the reaction during reductionas embodied in the specification referred to, that is, using from `50%to 150% calcium in excess, over the theoretical required in thereaction, together with calcium chloride, to control localized hightemperatures duringthe reaction.

The inventors in the referred-to application found that the heat ofreaction and, therefore, the maximum temperature can be bettercontrolled by employing the oxide of vanadium, or other compoundthereof, in which .the valence of the vanadium is less vthan four,together with the addition of carefully dehydrated calcium .chloride ormagnesium chloride to the .charge .of oxide and calcium and/ ormagnesium. By reducing the heat of thereaction by using a lower valencecompound of vanadium and by dilutingthe charge with calciumchlor'ide.,they "haye'iheen able to produce consistently a non-pyrophoric vanadiumpowder substantially all of which is usable for the. production ofcoherentl ductile vanadium by the powder Vmetallurgy process.

The vanadous or hypo-vanadous oxide, or other .compound of vanadium tobe employed, in which .the valence of vanadium is not more .than three,maybe prepared, if not procurableby purchase, from pure vanadium-pe11toxide, ammonium metavanadate, NH4VO3., 0.1'v other vanadic compoundcontaining no harmful constituent, .by hydrogen reduction at 500 C.. tol00.0 C..as in a metal or ceramic boat in arefractory tub'efurnace.

.However, it is a well-known fact that oxygen and nitrogen ypresent inthe lattice structures of certain metals will result in excessive valuesof hardness, ,poor vductility., and diicult workability. It Vis usually.accepted that nitrogen 1s the more serious contaminant and, in thecaseof vanadium, this has been experimentally shown -to be true. Inaddition, the corrosion resistance of .armetalis dependent uponthedegree of contamination by these -two elements. Again nitrogen appearsas the more serious oender.

The basic operations `involved ,in the disclosure of the aforementionedapplication .are these:

.(a) AReduction of vanadium ipcntoxide tov vanadium trioxide withhydrogen gas at elevated tem erat e (som-100.0D 0.). p fus (b) Reductionof vanadium .trioxide Yto vanadium :metal powder with moltencalcium-metalrat elevated 'temperatures (900'-l350 C.).

V203+3Ca-l-(CaCl2)# 2V-}3CaO-|(CaClz) (2) The present improvement isconcerned with variations and/or amendments to step (a) which tend toreduce the nitrogen content. As Vpreviously performed, dry commercialhydrogen was admitted to .the reaction furnace and the reductionadjudged complete' fat such time as the product conforms to theproperties-of vanadium trioxide. However, thisproduct is frequentlyfound to contain higher .percentages `of .nitrogen than would be theexpected from consideration of the nitrogen content of the pentoxide'.This maybe ascribed to the fact that commercial hydrogen contains inexcess of 0.1 volume percent of nitrogen. This nitrogen 'is' combinedwith hydrogen to `formainmonia on the surface' of oxides of vanadium.Vanadium trioxide reacts readily with am- I have determinedtheoretically that this reaction, will produce a vanadium trioxide whichwill contain quantities of nitrogen in direct relation to thetemperature of the reduction illustrated by Equation 1. Briey it may bestated that vanadium pentoxide reduced atV 1000 C. in commercialhydrogen will produce trioxide containing 0.1% by weight of nitrogen. Ifthe same reaction is caused to occur at 600 C. the resulting trioxidewill contain less than 0.001% nitrogen. This is shown graphically in thesole figure.

Therefore, during the normalV reduction in accordance with Equation 1,suflicient nitrogen passes over the V203 to contaminate it to themaximum extent permitted by the equilibrium of the equation Knowing thatnitrogen is deleterious to vanadium metal, and knowing that most of thenitrogen in V203 is carried over in the calcium reduction of thetrioxide to produce a metal contaminated with nitrogen, the equilibriumof Equation 4 was studied theoretically and the findings illustrated inthe curves of the sole ligure were verified analytically.

It Was evident that the temperature of reduction was critical and shouldbe maintained below 650 C. or between 450 and 650 C., in order to keepthe nitrogen in the ultimate metal product to the lowest possibleconcentration. The melting points of the triand pentoxides are above 650C., and therefore, more efficient reduction might also be expected belowthis temperature, as without the complication of a molten phase.

Further consideration of Equation 4 showed that the principle of LeChatelier-Braun (mass-action) could be applied, since increasing theconcentration of H2O on the right hand side of said Equation 4 willdecrease the equilibrium concentration of VN, thereby furthereliminating nitrogen. Thus the dewpoint of the hydrogen should bespecified as above C. and preferably from 40 to 60 C. It thus containsmore than 4.8 and preferably from 51.1 to 130.5 mg. of water per liter,according to Properties of Saturated Steam, Handbook of Chemistry andPhysics, 28th edit. Chemical Rubber Publishing Co., 1944. Hydrogenreceived from factory sources is usually dried to 30 C. A combination ofcontrolled reduction temperature, and controlled humidity of hydrogenis, therefore, the preferred embodiment, although the separate use ofeither feature involves an improvement over prior practice. For example,the mere humidilication of the hydrogen used in the practice of theinvention of the Gregory et al. application, previously referred to, isbeneficial.

Improvement in the quality of V203, initially high in nitrogen asreceived from supplier' or as prepared, may be yaccomplished by heatingto 650 C. or less under the same humidity conditions as proposed in thepreceding paragraph, using hydrogen, argon, or helium as a carrier gasfor the water vapor.

Vanadium metal produced from the purer trioxide by step (b) of theprevious disclosure has been found to be softer than any previousproduct (VPNso (Vickers Pyramid No. with a 30 kg. load) l50 vs.'240)(Rockwell 81 vs. Rockwelln 100) and it may be formed at roomtemperature, whereas the previous'product must be elevated to 600 C. inan inert atmosphere and formed gradually with frequent reheating.

' The above may be ampliied by the following tabular information:

Thus the vanadium metal will be more seriously contaminated than isindicated by the figure which refers to V203.

The lower curve of the figure represents an equilibrium of idealconditions, i. e., properly humidied hydrogen and controlledtemperatures. Actually, the two curves indicate the fact that:

(a) Without humidication, temperature control is effective since theupper curve will have the same favorable slope, but will be displaced tohigher values of nitrogen content.

(b) With humidication of the hydrogen, the lower curve representsappropriate upper limits for nitrogen content. Lower or vanishing valuesof nitrogen content may, of course, be obtained provided the vanadiumpentoxide used is free of nitrogen and the hydrogen used for reductionis of extreme purity. However, the prices of such extremely purereagents are prohibitive.

Although a preferred embodiment has been described, it will beunderstood that modifications may be made within the spirit and scope ofthe invention. For example, although we have specically considered thepreparation of only vanadium trioxide and its improvenient by watervapor, I do not wish to be limited to this compound for, as previouslyexplained, similar considerations apply to oxides, such as the dioxide,V202, in which the vanadium has a valence of less than four.

Also, if it were desired to eliminate vanadium nitride from the dioxide,or other vanadous or hypo-vanadous compound, Equation 4 would apply inits improvement by the use of water Vapor, except that the vanadiumnitride upon being denitrided would appear as the dioxide or othervanadous or hypo-vanadous compound, on the left hand side of theequation, rather than the trioxide. In the same Way, Equation 2 isapplicable, using such vanadous or hypo-vanadous compound other than thetrioxide, the amount of the calcium, or other reducing element, and thechloride being changed proportionately to agree with the lower oxideratio in the compound being reduced.

I claim:

l. The method of producing vanadium trioxide containing less than .1% byweight of nitrogen, comprising holding vanadium pentoxide in hydrogeninitially containing water in vapor form and in the range between 4.8and 130.5 mg. per liter, and heating to a temperature above 450 C. butnot higher than 650 C. until the reaction is complete.

2. The method of producing vanadium trioxide containing less than .1% byweight of nitrogen, comprising reducing vanadium pentoxide in a reactionchamber with hydrogen gas containing some nitrogen and initiallysaturated at a temperature between 0 C. and 60 C. with water vapor,while maintaining said chamber until the reaction is complete attemperatures above 350 C. and belowl 650 C.

3. The method of producing vanadium trioxide containing less than .1% byweight of nitrogen, comprising reducing vanadium pentoxide by heating itin hydrogen initially humidied with water vapor to a dew point higherthan 0 C. but not higher than 60 C. and at a temperature in the rangebetween 450 C. and 650 C. until the reaction is complete.

4. The method of producing vanadium trioxide containing less than .1% byweight of nitrogen, comprising reducing vanadium pentoxide by heating toa temperature above 350 C. in commercial hydrogen containing nitrogen asan impurity, but preventing said nitrogen from being fixed in theproduct to an undesired extent by initially humidifying said hydrogen toa dew point between 40 C. and 60 C., and preventing vthe temperature ofreaction until complete from going higher than 650 C.

5. The method of producing vanadium trioxide containing less than .1% byweight of nitrogen, comprising reducing vanadium pentoxide by heating itto a temperature between 350 C. and 650 C. in hydrogen initiallyhumidited with water vapor to a dew point higher than 0 C. but nothigher than 60 C. until the reaction is complete.

6. The method of producing vanadium trioxide containing less than .1% byweight of nitrogen, comprising reducing vanadium pentoxide by heating toa temperature between 350 C. and 650 C. in commercial hydrogencontaining nitrogen as an impurity until the reaction is complete, butpreventing said nitrogen from being xed in the product to an undesiredextent by humidifying said hydrogen to an initial dew point between 40"C. and 60 C., whereby it contains between 51.1 and 130.5 mg. of waterper liter.

7. The method of producing vanadium oxide containing less than .1% byweight of nitrogen, in which the vanadium has a valence of less thanfour, comprising reducing vanadium pentoxide in a reaction chamber withhydrogen gas containing some nitrogen and initially saturated at atemperature between 0 C. and 60 C. with water vapor, while maintainingsaid chamber at temperatures below 650 C. but higher than about 350 C.so as to be high enough to allow the reaction to occur at a reasonablerate until the reaction is complete.

8. The method of producing vanadium oxide containing less than .1% byweight of nitrogen, in which the vanadium has a valence of less thanfour, comprising reducing vanadium pentoxide by heating it in hydrogeninitially humidied with Water vapor to a dew point higher than 0 C. butnot higher than 60 C. and at a temperature in the range between 450 C.and 650 C. until the reaction is complete.

References Cited in the le of this patent UNITED STATES PATENTS BecketSept. 17, 1907 OTHER REFERENCES I. W. Mellor: Inorganic and TheoreticalChemistry, vol. 9, 1929, page 752, Longmans, Green and Co., N. Y. Haslamand Russel: Fuels and Their Combustion, 1926, page 567. McGraw-Hill, N.Y., publishers.

Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry,vol. 9, pages 739, 740, 741, 743, 744.

1. THE METHOD OF PRODUCING VANADIUM TRIOXIDE CONTAINING LESS THAN 1% BYWEIGHT OF NITROGEN, COMPRISING HOLDING VANADIUM PENTOXIDE IN HYDROGENINITIALLY CONTAINING WATER IN VAPOR FORM AND IN THE RANGE BETWEEN 4.8AND 130.5 MG. PER LITER, AND HEATING TO A TEMPERATURE ABOVE 450* C. BUTNOT HIGHER THAN 650* C. UNTIL THE REACTION IS COMPLETE.